Pressurized catalytic production of dioxide species

ABSTRACT

A packed bed catalyst in a pressurized vessel/reactor during contact with a dioxide species precursor enhances catalytic conversion of the precursor to the dioxide species, compared with the same catalytic conversion performed in a non-pressurized vessel/reactor.

FIELD OF THE INVENTION

The present invention relates to generating aqueous chlorine dioxidefrom chlorine dioxide precursors. In particular, the present inventionrelates to catalytically converting one or both of aqueous chlorous acidand aqueous chloric acid to aqueous chlorine dioxide.

BACKGROUND OF THE INVENTION

Chlorine dioxide (molecular formula ClO₂) is a well-known disinfectantand cleanser that can be generated using chlorous acid as a startingmaterial. Chlorous acid (molecular formula HClO₂) occurs when there isan essentially complete substitution of the counter cation of the anionchlorite (ClO₂ ⁻) with hydrogen ion (H⁺). Chloric acid (molecularformula HClO₃) occurs when there is an essentially complete substitutionof the counter cation of the anion chlorate (ClO₃ ⁻) with hydrogen ion(H⁺).

The generation of aqueous chlorous acid by the acidification of anaqueous chlorite salt solution (sometimes misnamed stabilized aqueouschlorine dioxide solution) is well known. In fact, whether an aqueoussolution contains a chlorite salt or chlorous acid depends upon thesolution pH, with chlorous acid being essentially exclusively present ata sufficiently low pH, e.g., at pH below 1.7, and chlorite salt beingexclusively present at a sufficiently high pH, e.g., at pH 8.5. Amixture of chlorous acid and chlorite salt is present at pH's inbetween. Below a pH of 4 chlorous acid predominates, and above that pH,chlorite is the predominate species. See Gilbert Gordon, “The Chemistryof Chlorine Dioxide,” Progress in Inorganic Chemistry: Volume 15, Ed. S.J. Lippard, 1972, 201-286 (Gordon), the disclosure of which isincorporated by reference as if fully set forth herein.

The speed of the catalytic reaction to chlorine dioxide depends on theratio of chlorous acid to chlorite in the aqueous solution. It Is alsoknown that, over time, aqueous chlorous acid slowly converts to chlorinedioxide. This slow conversion predominates in solutions containing lowacid and high chlorite concentrations, making the reaction difficult tocontrol, especially in high alkalinity water supplies. It is furtherwell known that in an oxidizing environment, such as in the presence ofchlorine or an anode, chlorine dioxide can be generated from chlorousacid.

U.S. Pat. No. 7,087,208 (hereinafter “US'208”), the disclosure of whichis incorporated by reference as if fully set forth herein, teachespacking a reaction vessel with water-insoluble, catalytic particles,continuously passing a stream of aqueous chlorous acid into the vesseland through the catalytic particles, thereby catalytically convertingthe chlorous acid in the stream to chlorine dioxide, and thencontinuously removing from the vessel the stream of aqueous (generated)chlorine dioxide.

SUMMARY OF THE INVENTION

Accordingly, the present invention provides an improvement in theaforesaid method of catalytically generating chlorine dioxide accordingto US '208. More precisely, it has been surprisingly discovered that bypressurizing the reaction vessel, either continuously or intermittently,while the catalytic particles are flooded with a chlorous acid/chloricacid solution significantly increases the conversion rate to chlorinedioxide.

Therefore, the present invention provides a process for generatingaqueous chlorine dioxide which comprises the steps of establishing orproviding a pressurizable reaction vessel holding a packed bed ofporous, water-insoluble catalytic particles and having a vessel inletand vessel outlet, continuously or intermittently feeding an aqueoussolution containing at least one of chlorous acid and chloric acidthrough the vessel inlet into contact with the packed bed of porous,water-insoluble catalytic particles under continuous or intermittentpressurization to produce an aqueous chlorine dioxide solution, andcontinuously or intermittently removing the thus produced aqueouschlorine dioxide solution from the vessel through the vessel outlet.

By pressurizing the reaction vessel, pressure is applied to the packedbed flooded with chlorous acid/chloric acid solution, such that littleor no fluidization of the packed bed occurs. Applying pressure to theacid feed or to the packed bed separately before contacting the bed withthe solution would not have the desired effect; pressure whethercontinuous or intermittent must be applied to the packed bed whenflooded with the acid solution in order to improve (increase) the rateof catalytically converting, i.a., aqueous chlorous acid into aqueouschlorine dioxide as taught in US '208.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows an exploded elevational view of a plastic tube (vessel)used in Examples 1 and 4.

FIG. 2 shows an exploded elevational view of a plastic tube and a ballvalve used in Examples 2 and 5.

FIG. 3 shows an exploded elevational view of a plastic tube and aback-pressure regulator used in Examples 3 and 6.

FURTHER DESCRIPTION OF THE INVENTION

As used herein the following terms will have the meanings stated. Theterm “chlorous acid” refers to a solution whereby there has been anessentially complete substitution of the counter cation of the anionchlorite (ClO₂ ⁺) with hydrogen ion (H⁺) (“aqueous chlorous acidsolution,” “aqueous chlorous acid,” and “chlorous acid solution” areused synonymously herein). According to Gordon, chlorous acidpredominately exists (over chlorite) in solution at a pH less than 4.The term “chloric acid” refers to a solution whereby there has been anessentially complete substitution of the counter cation of the anionchlorate (ClO₃₊) with hydrogen ion (H⁺) (“aqueous chloric acidsolution,” “aqueous chloric acid,” and “chloric acid solution” are usedsynonymously herein). Similar to chlorous acid, an aqueous chloric acidsolution predominately exists (over chlorate) at a pH less than 4. Theterm “water-insoluble” means a substance incapable of being dissolved.The term “packed bed of . . . particles” means water-insoluble particlesheld together in constant contact with each other, such as, e.g.,contained in a tube, pipe, or other vessel filled (completely) with theparticles. The term “acid solution” refers to either a chlorous acidand/or chloric acid solution.

In accordance with the present invention, feeding of acid solution andremoving of chlorine dioxide solution are at the same rate and at thesame regular or irregular intervals. Feeding and removing can occur overintervals ranging as low as about 1 second to as long as about 1 week;however, the feeding and removing are preferably carried outcontinuously. The feeding and removing rates of the solutions fed to andremoved from the reaction vessel containing the catalytic particles willdepend at least in part upon the size of the reaction vessel and relatedequipment and can be readily determined by those skilled in the art. Thepressure applied to the reaction vessel containing the catalyticparticles and the chlorous acid and chloric acid solution to beconverted should best be applied within the range of about 5 psi andabout 250 psi, and preferably between about 25 psi and 60 psi. Theporous, water-insoluble catalytic particles have particle sizes ranginggenerally about 4 to about 50 US mesh, preferably about 4 to about 40 USmesh. The catalytic particles must be water-insoluble to ensure the bedstays packed.

The porous, water-insoluble catalytic particles are completely made ofone or more water insoluble catalysts, or made of porous,water-insoluble inorganic particles having one or more water-insolublecatalysts deposited thereon in a waterproof manner. How to obtain boththe particles completely made of one or more water insoluble catalysts,and those made of porous, water-insoluble inorganic particles having oneor more water-insoluble catalysts deposited thereon in a waterproofmanner will be readily apparent to one of ordinary skill in the art.Exemplary catalysts include platinum group metals, platinum group metaloxides, transition group metals, and transition group metal oxides.Preferred catalysts include platinum, palladium, manganese dioxide,carbon, and ion exchange material. Suitable commercially availablecatalysts include inorganic cation resin in the hydrogen form havingplatinum catalyst placed on the surface of the inorganic cation resinsold by ResinTech Inc. at 160 Cooper Rd, West Berlin, N.J. under thename Resintech SIR-600 and inorganic clay having platinum catalystplaced on the surface of the inorganic clay sold by Wateropolis Corp. on12375 Kinsman Rd, Newbury Township, Ohio under the name Ceralite-A.

Referring now to FIG. 1, there is shown a basic vessel used to contain apacked bed catalytic material. The catalytic material can be packed insuch way that the particles are compacted and are in contact with eachother. This packed bed is contained within the basic vessel such thatthe inlet and outlet prevent the packed material from being able toleave the vessel.

In the embodiment shown in FIG. 2, the packed vessel is pressurized andmaintained using a ball valve. This pressure on the packed catalyticmaterial held within the vessel can be produced using any means so as toensure that constant pressure, either continuous or intermittent, isbeing applied to the packed vessel.

In the embodiment shown in FIG. 3, a catalytic material is held within apacked vessel and to which constant pressure is maintained by use of aback-pressure regulating valve. The packed vessel can be held underpressure, either continuous or intermittent, during the generation ofaqueous chlorine dioxide by any means that will keep said pressure onthe packed vessel constant or nearly constant.

Plastic tubes used for carrying out the tests set forth in Examples 1-6below are shown in FIG. 1, FIG. 2, and FIG. 3 where numerals in thedrawings refer to like parts throughout. The plastic test tube 100includes a generally cylindrical body 102 having a conventionalconnection closure mounted at each end thereof in the form of an inletupper end connection 104 and an outlet lower end connection 106. PVC(polyvinyl chloride) screens 108 which fit over the inner diameter ofthe cylindrical tube 102 are glued at each end between the end of thecylindrical tubing 102 and the end closures 104 and 106 to act assupport for the packed-bed filling. Outlet tubing 112 runs from theoutlet end connection 106 (see FIGS. 2 and 3). A true union ball valve200 manufactured by Spears at 15853 Olden St, Sylmar, Calif., isconnected to the tubing downstream of the packed vessel 102 to start andstop the removal of the stream of chlorous acid. An M-Seriesback-pressure valve 300 manufactured by Griffco Valve, Inc. at 188Creekside Drive, Amherst, N.Y., is set to 25 psi downstream of thepressure vessel to apply back-pressure to the solution.

Precursor Solution: In Examples 1-6, a chlorite precursor solution isused for each set of Examples. The chlorite precursor solution isprepared by diluting an aqueous 25% active sodium chlorite solution withreverse osmosis water to a concentration of 1250 ppm. Before beginningeach of the following examples, the chlorite precursor solution isconverted to chlorous acid by appropriate acidification. In example 7-8,a chlorate precursor solution is used for each set of Examples. Thechlorate precursor solution is prepared by dissolving powdered sodiumchlorate into reverse osmosis water to achieve a concentration of 1250ppm. A powdered sodium bisulfite solution is then mixed into thechlorate precursor solution. The powdered sodium bisulfite solutionweighed to be 1.33 more than what the powdered sodium chlorate weighed.

EXAMPLE 1 Gravity Flow With SIR Catalyst

Chlorine dioxide is generated by gravity feeding chlorous acid through a30 ml plastic tube 102 as shown in FIG. 1. The tube is packed with thecommercially available Resintech SIR-600 catalyst described above, suchthat the tube is full. A 10 ml sample of the chlorous acid solution at apH of 1.8 as converted from the sodium chloride precursor solution isthen poured into the plastic tube at atmospheric pressure and collectedat atmospheric pressure as the solution comes out of the plastic tube.The flow through of the sample takes only a few seconds. The 10 mlsample of solution is taken from the outlet connection 106, and a HachSpectrophotometer is used for the measurement of the chlorine dioxideconcentration immediately after the sample is collected. The foregoingtest was repeated with four additional 10 ml samples. Table 1 recordsthe chlorine dioxide concentration conversion as measured for each ofthe 5 trials.

EXAMPLE 2a Static Contact Time Test With SIR Catalyst

One 30 ml plastic tube with a ball valve 200 on the downstream side oftubing 112 as shown in FIG. 2 is clipped to a wall with pipe clips. Thetube is packed with the same Resintech SIR-600 catalyst as in Example 1,such that the tube is full. The chlorous acid solution at a pH of 1.8 asconverted from the sodium chloride precursor solution is then fed intothe plastic tube at atmospheric pressure, and once the packed bed isflooded the ball valve 200 is closed. The solution stayed within thepacked bed catalyst open to atmospheric pressure for five minutes. Thechlorous acid solution is then removed at atmospheric pressure andcollected and a Hach Spectrophotometer is used for the measurement ofchlorine dioxide immediately after the sample is collected. The chlorinedioxide concentration conversion is recorded in Table 1.

EXAMPLE 2b Static Pressure Test With SIR Catalyst

One 30 ml plastic tube with a ball valve 200 on the downstream side oftubing 112 as shown in FIG. 2 is clipped to a wall with pipe clips. Thetube is packed with the same Resintech SIR-600 catalyst as in Examples 1and 2a, such that the tube is full. The chlorous acid solution at a pHof 1.8 as converted from the sodium chloride precursor solution is thenfed into the plastic tube. Once the packed bed is flooded with thechlorous acid solution the ball valve is closed, and the inlet pressureis increased to a pressure of 60 psi. The solution stays under staticpressure at 60 psi in the plastic tube for five minutes. The chlorousacid solution is then removed and collected and a Hach Spectrophotometeris used for the measurement of chlorine dioxide immediately after thesample is collected. The chlorine dioxide concentration conversion isrecorded in Table 1.

EXAMPLE 3 Dynamic Pressure Test With SIR Catalyst

One 30 ml plastic tube with a back-pressure regulator 300 on thedownstream side of tubing 112 as shown in FIG. 3 is clipped to a wallwith pipe clips. The tube is packed with the same Resintech SIR-600catalyst as in Examples 1, 2a and 2b, such that the tube is full. A backpressure is applied continuously by regulator 300 at a constant pressureof 25 psi. The chlorous acid solution at a pH of 1.8 as converted fromthe sodium chloride precursor solution is then continuously fed into thepacked tube and removed at the same rate it is being fed. Five samplesare taken every 5 minutes. These samples are measured for chlorinedioxide with a Hach Spectrophotometer immediately after each sample iscollected. The chlorine dioxide concentration conversion is recorded inTable 1.

EXAMPLE 4 Gravity Flow With Clay Catalyst

The five trials set forth in Example 1 are here repeated, except the 30ml plastic tube is packed with the commercially available inorganic clayCeralite-A catalyst described above, such that the tube is full. A 10 mlsample of chlorous acid solution at a pH of 1.8 as converted from thesodium chloride precursor solution then poured into the plastic tube atatmospheric pressure and collected at atmospheric pressure as thesolution comes out of the plastic tube, and a Hach Spectrophotometer isused for the measurement of chlorine dioxide immediately after thesample is collected. Table 2 records the chlorine dioxide concentrationconversion as measured for each of the five trials.

EXAMPLE 5a Static Contact Time Test With Clay Catalyst

The test set forth in Example 2a is here repeated, except the 30 mlplastic tube is packed with the same Ceralite-A catalyst as used inExample 4, such that the tube is full. The chlorous acid solution at apH of 1.8 as converted from the sodium chloride precursor solution isthen fed into the plastic tube at atmospheric pressure, and once thepacked bed is flooded the ball valve 200 is closed. The solution stayedwithin the packed bed catalyst open to atmospheric pressure for fiveminutes. The chlorous acid solution is then removed at atmosphericpressure and collected; and a Hach Spectrophotometer is used for themeasurement of chlorine dioxide immediately after the sample iscollected. The chlorine dioxide concentration conversion as measured isrecorded in Table 2.

EXAMPLE 5b Static Pressure Test With Clay Catalyst

The test set forth in Example 2b is here repeated, except the 30 mlplastic tube is packed with the same Ceralite-A catalyst as used inExample 4, such that the tube is full. The chlorous acid solution at apH of 1.8 as converted from the sodium chloride precursor solution isthen fed into the plastic tube, and once the packed bed is flooded theball valve 200 is closed, and the inlet pressure is increased to apressure of 60 psi.

The solution stays under static pressure at 60 psi in the plastic tubefor five minutes. The chlorous acid solution is then removed andcollected and a Hach Spectrophotometer is used for the measurement ofchlorine dioxide immediately after the sample is collected. The chlorinedioxide concentration conversion as measured is recorded in Table 2.

EXAMPLE 6 Dynamic Pressure Test With Clay Catalyst

The test set forth in Example 3 is here repeated, except the 30 mlplastic tube with back-pressure regulator 300 on the downstream side asshown in FIG. 3 is packed with the same Ceralite-A catalyst placed asused in Examples 4, 5a and 5b, such that the tube is full. A backpressure is applied continuously at a constant pressure of 25 psi. Thechlorous acid at a pH of 1.8 as converted from the sodium chlorideprecursor solution is then continuously fed into the packed tube andremoved at the same rate at which it is being fed. Five samples aretaken each every 5 minutes. These samples are measured for chlorinedioxide with a Hach Spectrophotometer immediately after each sample iscollected. Table 2 records the chlorine dioxide concentration conversionas measured for each of the five samples.

EXAMPLE 7 Gravity Flow Test With SIR Catalyst

One 30 ml plastic tube with a ball valve on the downstream side as shownin FIG. 2 is clipped to a wall with pipe clips and is packed with thesame Resintech SIR-600 catalyst as used in Examples 1-3, such that thetube is full. A 10 ml sample of the chlorous acid solution at a pH of1.8 converted from the chlorite precursor solution is then poured intothe plastic tube and collected as the solution comes out of the plastictube. The 10 ml sample of solution is taken, and a HachSpectrophotometer is used for the measurement of the chlorine dioxideconcentration immediately after the sample is collected. The above testis repeated an additional eleven times at five minute intervals. Table 3shows the average concentration of the twelve (12) samples over a 55minute period.

EXAMPLE 8 Dynamic Pressure Test With SIR Catalyst

One 30 ml plastic tube with a back-pressure regulator on the downstreamside as shown in FIG. 3 is clipped to a wall with pipe clips and ispacked with the same Resintech SIR-600 catalyst used in Examples 1-3 and7, such that the tube is full. Back pressure is applied continuously ata constant pressure of 25 psi. The chlorous acid solution converted fromthe chlorite precursor solution is then continuously fed into the packedtube and the existing solution is removed at the same rate. Samples aretaken every 5 minutes for an hour for a total of 12 samples. These 12samples are measured for chlorine dioxide with a Hach Spectrophotometer.The average is displayed in Table 3.

TABLE 1 Example 1 Example 2a Example 2b Example 3 ClO₂ % ClO₂ % ClO₂ %Time ClO₂ % Trial Concentration Conversion Trial ConcentrationConversion Trial Concentration Conversion (min) Concentration Conversion1 329 35.9 1 599 65.4 1 732 79.8 0 748 80 2 553 60.3 5 764 80 3 575 62.710 779 80 4 593 64.7 15 770 80 5 584 63.7

TABLE 2 Example 4 Example 5a Example 5b Example 6 ClO₂ % ClO₂ % ClO₂ %Time ClO₂ % Trial Concentration Conversion Trial ConcentrationConversion Trial Concentration Conversion (min) Concentration Conversion1 431 47.6 1 551 60.1% 1 733 80 0 823 80 2 472 52.2 5 824 80 3 466 51.510 822 80 4 423 46.8 15 809 80 5 524 58.0

TABLE 3 AVG CIO₂ Concentration Over 1 Hour Example 7  5 mg/L Example 832 mg/L % Increase 540%

1-9. (canceled)
 10. A process for generating aqueous chlorine dioxidecomprising the steps of: providing a pressurizable vessel holding apacked bed of porous, water-insoluble catalytic particles capable ofconverting chlorous acid and chloric acid to chlorine dioxide, saidvessel having an inlet and an outlet; continuously or intermittentlyfeeding an aqueous solution containing at least one of chlorous acid andchloric acid at a pH less than 4 through the vessel inlet into contactwith the packed bed of porous, water-insoluble catalytic particles undercontinuous or intermittent pressurizing to produce an aqueous chlorinedioxide solution; and continuously or intermittently removing saidproduced aqueous chlorine dioxide solution from the packed bed and thevessel through the vessel outlet.
 11. The process of claim 10 whereineach of the feeding, removing, and pressurizing is continuous.
 12. Theprocess of claim 10 wherein each of the feeding, removing, andpressurizing is intermittent.
 13. The process of claim 10, wherein thecontinuous or intermittent pressurizing of the catalytic particles isbetween about 5 psi and about 250 psi.
 14. A process for generatingaqueous chlorine dioxide comprising the steps of: providing apressurizable vessel filled with a packed bed of porous, water-insolublecatalytic particles capable of converting a precursor selected from thegroup consisting of at least one of chlorous acid and chloric acid tochlorine dioxide, said vessel having an inlet and an outlet; feeding ata rate to the packed bed, through the vessel inlet, an aqueous solutioncontaining the precursor at a pH less than 4 to flood the packed bedwith the aqueous precursor solution in order to convert the precursor tochlorine dioxide, pressurizing the flooded packed bed in the vessel to apressure greater than applied in the feeding step, to increase theconversion rate of the precursor to chlorine dioxide, and thereafterremoving the aqueous chlorine dioxide from the packed bed through thevessel outlet at the same rate as the feeding step.
 15. The process ofclaim 14 wherein the catalytic particles are selected from the groupconsisting of platinum group metals, platinum group metal oxides,transition group metals, and transition group metal oxides.
 16. Theprocess of claim 14 wherein the catalytic particles are selected fromthe group consisting of platinum, palladium, manganese dioxide, carbon,and ion exchange material.
 17. The process of claim 14 whereinpressurizing the flooded packed bed in the vessel is at a pressurebetween about 5 psi and about 250 psi.
 18. The process of claim 14wherein the feeding, pressurizing, and removing steps are continuous.19. The process of claim 18 wherein the pressurizing step is effected bycontinuously applying a back pressure through the vessel outlet whilecontinuously removing the aqueous chlorine dioxide at the same rate ascontinuously feeding the aqueous precursor solution.
 20. The process ofclaim 18 wherein pressurizing the flooded packed bed in the vessel is ata pressure between about 5 psi and about 250 psi.
 21. The process ofclaim 18 wherein the catalytic particles are selected from the groupconsisting of platinum group metals, platinum group metal oxides,transition group metals, and transition group metal oxides.
 22. Theprocess of claim 14 wherein the feeding and removing steps areintermittent, occurring at the same regular or irregular intervals, andthe pressurizing step is intermittent.
 23. The process of claim 22wherein the pressurizing step is effected by intermittently haltingremoving the aqueous chlorine dioxide from the vessel outlet andcontemporaneously increasing pressure applied to the flooded bed throughthe vessel inlet.
 24. The process of claim 22 wherein pressurizing theflooded packed bed in the vessel is at a pressure between about 5 psiand about 250 psi.
 25. The process of claim 22 wherein the catalyticparticles are selected from the group consisting of platinum groupmetals, platinum group metal oxides, transition group metals, andtransition group metal oxides.
 26. A system for generating aqueouschlorine dioxide comprising: a pressurizable vessel filled with a packedbed of porous, water-insoluble catalytic particles capable of convertinga precursor selected from the group consisting of at least one ofchlorous acid and chloric acid to chlorine dioxide, said vessel havingan inlet and an outlet; a device in fluid communication with the vesseloutlet for increasing pressure in the vessel to a pressure greater thanapplied when feeding an aqueous solution to the packed bed, through thevessel inlet.
 27. The system of claim 26 wherein the catalytic particlesare selected from the group consisting of platinum group metals,platinum group metal oxides, transition group metals, and transitiongroup metal oxides.
 28. The system of claim 26 wherein the device is aball valve.
 29. The system of claim 26 wherein the device is aback-pressure regulator.